Method of controlling internal combustion engine

ABSTRACT

The invention provides a control method of intending to improve a heat efficiency by an Atkinson cycle, improve a charging efficiency, improve an efficiency of a supercharger and increase a freedom of cam design. In particular, the invention relates to a control method of opening and closing a valve in an internal combustion engine with supercharger. An effective compression ratio is decreased by temporarily re-opening an exhaust valve in a compression stroke first stage, whereby a heat efficiency is improved without excessively increasing a cylinder internal pressure. Preferably, an exhaust valve re-opening time is set such that the effective compression ratio/expansion ratio is within a range from 0.5 to 0.9. Further, an exhaust valve is not temporarily opened in a compression stroke first stage, at a time of starting or driving under a low load, and the Atkinson cycle in accordance with the re-opening of the exhaust valve is achieved at a time of driving under a high load.

TECHNICAL FIELD

[0001] The present invention relates to a control method of an internalcombustion engine, and more particularly to a control of opening andclosing a valve in an internal combustion engine provided with asupercharger.

BACKGROUND ART

[0002] As a method of improving a heat efficiency of an internalcombustion engine, the following methods have been conventionallyemployed.

[0003] [Conventional Method 1] method of increasing maximum cylinderinternal pressure

[0004] This method corresponds to a method of increasing a maximumcylinder internal pressure so as to improve a heat efficiency, by makinga compression ratio high and making a supercharging high.

[0005] [Conventional Method 2] method of increasing expansion ratio ofengine

[0006] It is possible to improve a heat efficiency by increasing anexpansion ratio of an engine.

[0007] [Conventional Method 3] method of achieving Atkinson cycle bydelayed closing of air supply valve or inlet valve

[0008]FIG. 23A shows an air supply stroke, FIG. 23B shows a first stageof a compression stroke, and FIG. 23C shows a later stage of thecompression stroke. A compression start time can be delayed by settingan air supply valve 1 in an open state until the compression strokefirst stage in which a piston 8 is ascended, and closing the air supplyvalve 1 at a later time than a normal time, as shown in FIG. 23B, at thesame time of increasing the compression ratio of the engine, whereby itis possible to reduce an effective compression ratio and it is possibleto obtain a large expansion ratio while restricting an excessiveincrease of the cylinder internal pressure. In this case, in FIGS. 23A,23B and 23C, reference numeral 2 denotes an air supply port, referencenumeral 3 denotes a combustion chamber, reference numeral 5 denotes anexhaust valve, and reference numeral 6 denotes an exhaust port. FIG. 24shows a change of an air supply valve lift in this method. The airsupply valve lift shown by a solid line corresponds to a case of thenormal cycle, and an air supply discharging period is secured tillclosely a middle of the compression stroke, by changing the air supplyvalve lift in the normal cycle to an air supply valve lift shape of thedelayed closing as shown by a broken line.

[0009]FIG. 25 shows an exhaust valve opening period and an air supplyvalve opening period of the internal combustion engine formed as theAtkinson cycle as shown in FIGS. 23A, 23B, 23C and 24, a range (a crankangle) denoted by reference symbol OL is an overlap period between theexhaust valve opening period and the air supply valve opening period,and a crank angle range θ2 is an air supply discharging period securedby the air supply valve delayed closing.

[0010]FIG. 26 is an Atkinson cycle indicator diagram in the internalcombustion engine in FIGS. 23A to 25, a compression work loadcorresponding to a hatched area is reduced in comparison with the normalcompression stroke shown by a broken line, by setting the air supplyvale closing time SC later than the normal one in the compression strokefirst stage. In this case, reference symbol EO denotes an exhaust valveopening time, reference symbol SO denotes an air supply valve openingtime, and reference symbol EC denotes an exhaust vale closing time. Inaccordance with the Atkinson cycle of this structure, it is possible toenlarge the expansion ratio while maintaining the maximum cylinderinternal pressure, it is possible to increase the expansion ratiowithout increasing the cylinder internal pressure, and it is possible toimprove the heat efficiency.

[0011] [Conventional Method 4] method of achieving Atkinson cycle on thebasis of early dosing of air supply valve

[0012]FIG. 27A shows an air supply stroke, FIG. 27B shows an air supplystroke later stage, and FIG. 27C shows a compression stroke. This methodis a method of achieving the Atkinson cycle by reducing an air supplyamount supplied within the combustion chamber 3 by closing the airsupply valve 1, and making the effective compression ratio small byreducing the compression stroke, in the air supply stroke later stage inwhich the piston 8 descends as shown in FIG. 27B.

[0013]FIG. 28 shows an exhaust valve opening period and an air supplyvalve opening period in the internal combustion engine shown in FIGS.27A, 27B and 27C. Reference symbol OL denotes an overlap period betweenthe exhaust valve opening period and the air supply valve openingperiod, and a crank angle θ3 is a crank angle (an angle of lead) betweenan air supply valve closing period and an air supply bottom dead centerBDC. In other words, the air supply valve 1 is early closed the crankangle θ3 before the air supply bottom dead center BDC.

[0014]FIG. 29 is an Atkinson cycle indicator diagram in the internalcombustion engine shown in FIGS. 27A, 27B, 27C and 28, a compressionwork load corresponding to a hatched area is reduced in comparison withthe normal compression stroke shown by a broken line, by quickening theair supply vale closing time SC to the air supply stroke later stage,whereby a gas exchange work load is reduced.

DISCLOSURE OF THE INVENTION

[0015] (Technical Problem to be Solved by the Invention)

[0016] In the method of increasing the maximum cylinder internalpressure in accordance with the conventional method 1, when the maximumcylinder internal pressure becomes too large, heat loss and a frictionloss are increased, and a lack of strength is generated in each of theportions, whereby an engine reliability is lowered. Accordingly, animprovement factor of the heat efficiency has a limit.

[0017] In the method of increasing the expansion ratio in accordancewith the conventional method 2, since the compression ratio issimultaneously increased in general, an increase of the maximum cylinderinternal pressure can not be avoided.

[0018] In the Atkinson cycle made by the delayed closing of the airsupply valve in accordance with the conventional method 3, the followingproblems are generated.

[0019] (a) Increase of Air Supply Temperature and Decrease of ChargingEfficiency

[0020] Since a part of the supply air which is once heated in thecombustion chamber is pushed back to the air supply port on the basis ofthe delayed closing effect of the air supply valve, the temperature ofthe supply air which is supplied in the next air supply stroke isincreased, and the charging efficiency is lowered.

[0021] (b) Decrease of Supercharger Efficiency at High SuperchargingTime

[0022] Since the air supply valve is opened in the compression strokefirst stage, a heated air pushed back to the air supply port from thecombustion chamber forms a resistance against the supply air from thesupercharger even when the supercharged pressure is increased byimproving a performance of the supercharger, whereby the load of thesupercharger becomes heavy. Accordingly, an air supply flow rate islimited and the efficiency of the supercharger is lowered. In the casethat the supply air pressure ratio is increased by increasing thesupercharged pressure in a state in which the supply air amount islimited, an engine position is changed from a current position B1 to aposition B2 as shown in FIG. 18, and the engine comes close to a surgingline B4 of the supercharger, so that there is a risk that a surging isgenerated.

[0023] (c) Wasteful Outflow of Supply Air

[0024] The closing time of the air supply valve is delayed for thepurpose of delaying the compression starting time, however, a shape ofan air supply cam is limited to a valve lift shape as shown by a brokenline in FIG. 24 in view of a design of the air supply cam shape, the airsupply valve is in a state of being largely open near the compressionbottom dead center BDC, and a large amount of air is flown out. Thewaster outflow of the supply air causes a reduction of output.

[0025] (d) Increase of Piston Loss

[0026] In the case of the internal combustion engine provided with thesupercharger, an air supply manifold pressure is higher than an exhaustmanifold pressure except the period exposed to the influence of theexhaust gas in the other cylinders. However, since the supply air ispushed back to the air supply port from the combustion chamber againstthe air supply manifold pressure, an ascending work load of the pistonbecomes high, the piston is hard to ascend, and the loss work isincreased.

[0027] In the method of early closing the air supply valve in accordancewith the conventional method 4, the following problems exist.

[0028] (a) Decrease of Lift Amount of Air Supply Valve

[0029] Since the lift period of the air supply valve is shortened, thelift amount of the air supply valve is limited geometrically at a timeof designing the cam, so that the flow of the supply air from the airsupply port to the combustion chamber is limited, and it is hard tosecure a sufficient air supply amount, thereby causing a reduction ofoutput.

[0030] (b) Decrease of Supercharger Efficiency

[0031] Since the air supply lift amount is limited in view of the camdesign, in accordance with the shortened air supply period, the airsupply amount is widely reduced, so that it is unavoidable to use astrong supercharger in order to secure the same air supply amount as thenormal one. However, since the air supply lift amount is small even byincreasing the supercharged pressure, the air supply amount is notincreased so much, so that the supercharger efficiency is lowered in thesame manner as that of the air supply valve delayed closing method, andcomes close to the surging line B4 of the supercharger as shown by theposition B2 in FIG. 12. Accordingly, there is a risk that the surging isgenerated.

[0032] (c) Increase of Gas Temperature Within Cylinder

[0033] Since the air supply valve is closed in the air supply strokelater stage, the increase of the gas temperature within the cylinder islarge, whereby the charging efficiency is lowered, and the compressionend temperature is also increased.

[0034] (Solving Method)

[0035] In order to solve the problems mentioned above, the presentinvention provides a method of controlling an internal combustion enginefor intending an Atkinson cycle of a combustion cycle by delaying acompression starting time with utilizing an exhaust valve, in place ofcontriving a closing time of the air supply valve, and in accordancewith the invention on the basis of a first aspect, there is provided amethod of controlling an internal combustion engine, wherein aneffective compression ratio is decreased by temporarily opening anexhaust valve in a compression stroke first stage at a time of drivingwhich it is neither at a time of starting nor at a time of driving undera low load.

[0036] In accordance with the invention on the basis of a second aspect,there is provided a method of controlling an internal combustion engineas recited in the first aspect, wherein an expansion ratio is set higher(in a range from 15 to 20) than a conventional engine, and an effectivecompression ratio is optionally changed within a range from 0.5 to 0.9times of the expansion ratio.

[0037] In accordance with the invention on the basis of a fourth aspect,there is provided a method of controlling an internal combustion engineas recited in the first or second aspect, wherein the internalcombustion engine is provided with a first exhaust cam having only a camcrest for an exhaust stroke, and a second exhaust cam having the camcrest for the exhaust stroke and a cam crest for again opening theexhaust valve in the compression stroke first stage, and both theexhaust cams are used so as to be freely switched.

[0038] In accordance with the invention on the basis of a fifth aspect,there is provided a method of controlling an internal combustion engineas recited in the first, second or fourth aspect, wherein the internalcombustion engine is provided with a first exhaust cam having only a camcrest for an exhaust stroke, and an auxiliary exhaust cam having only acam crest for again opening the exhaust valve in the compression strokefirst stage, and the method freely switches a single drive by means ofthe first exhaust cam, and a parallel drive by means of the firstexhaust cam and the auxiliary exhaust cam.

[0039] (Operative Effect in Comparison with Conventional Art)

[0040] In accordance with the present invention, since the Atkinsoncycle is achieved by temporarily opening again the exhaust valve in thecompression stroke first stage so as to delay the compression startingtime and make the effective compression ratio small, without delayingand quickening the closing time of the air supply valve, as is differentfrom the conventional Atkinson cycle, it is possible to achieve a highexpansion ratio while restricting the increase of the maximum cylinderinternal pressure, and achieve an improvement of the heat efficiency,and the following effect can be obtained.

[0041] (1) Since the exhaust valve is re-opened in the compressionstroke first stage, the freedom of designing the cam can be maintained,and it is possible to design such as to accurately relieve a necessaryair amount to the exhaust port at a necessary time, in comparison withthe Atkinson cycle ratio in accordance with the conventional air supplyvalve delayed closing or early closing. In other words, in comparisonwith the air supply valve delayed closing method, it is possible toeasily design such as to prevent a large amount of supply air from beingrelieved at the compression bottom dead point, and in comparison withthe air supply valve early closing method, it is possible to design suchas to sufficiently secure the air supply lift amount.

[0042] (2) Since a part of the supply air supplied to the combustionchamber is discharged to the exhaust port, the supply air discharged inthe manner mentioned above does not generate any resistance against thepressure supply air entering into the combustion chamber from the airsupply port even in the case that the performance of the supercharger isimproved and the supercharged pressure is increased. Accordingly, it ispossible to sufficiently secure the supply air flow rate, the load ofthe supercharger is lightened, and the efficiency of the supercharger isimproved. In other words, since it is possible to increase the airsupply flow rate even in the case that the supercharged pressure isincreased, the position gets away from the surging line B4 of thesupercharger as shown by the position B3 in FIG. 18, there is no fearthat the surging is generated, and it is possible to efficiently utilizethe supercharger.

[0043] (3) Since a part of the supply air supplied to the combustionchamber is discharged to the exhaust port, it is possible to prevent thesupply air temperature in the air supply port from being increased, incomparison with the delayed dosing method of the air supply valve,whereby it is possible to prevent the charging efficiency from beinglowered.

[0044] (4) Since a part of the supply air is relieved to the exhaustport so as to cool the exhaust system by re-opening the exhaust valve inthe compression stroke first stage, it is possible to shorten theoverlap period between the air supply valve opening period and theexhaust valve opening period while fixing the heat load of the exhaustsystem. Since it is possible to shorten the overlap period while fixingthe heat load of the exhaust system as mentioned above, it is possibleto increase the gas work exchange amount as shown in FIG. 21, and it ispossible to increase the cylinder residual gas as shown in FIG. 22 so asto intend to reduce NOx on the basis of an internal EGR effect.

[0045] (5) In a multiple cylinder internal combustion engine withsupercharger, an exhaust manifold pressure is lower than an air supplymanifold pressure except a time affected by the exhaust gas in the othercylinders. Since a part of the supply air is discharged to the exhaustmanifold, it is possible to restrict an ascending work amount of thepiston to a low level in comparison with the air supply valve delayedclosing method, so that it is possible to make the piston loss small.

[0046] (6) It is possible to introduce an exhaust pulse from the othercylinders in the case of well aligning the timing and the piping, bytemporarily opening the exhaust valve in the compression stroke firststage. Accordingly, it is possible to obtain the internal EGR effect soas to intend to prevent the NOx from being reduced or increased.

[0047] (7) It is possible to increase the heat efficiency whilemaintaining the cylinder internal pressure by making the expansion ratiohigh and setting the effective compression ratio within a range from 0.5to 0.9 times of the expansion ratio. Further, it is possible to inhibita smoke from being generated, by restricting the reduction of an excessair factor and making a combustion injection pressure high.

[0048] (8) If the exhaust valve is set such as not to be opened in thecompression stroke first stage, at the starting time or the low loadoperating time, it is possible to sufficiently secure an evaporation ofthe fuel, and it is possible to maintain a starting performance and alow load operating performance. On the other hand, at the high loadtime, it is possible to achieve an improvement of the heat efficiency byre-opening the exhaust valve in the exhaust stroke first stage andmaking the Atkinson cycle.

[0049] (9) In the case that the internal combustion engine is providedwith the first exhaust cam having only the cam crest for the exhauststroke, and the second exhaust cam having the cam crest for the exhauststroke and the cam crest for re-opening the exhaust valve in thecompression stroke first stage, and both the exhaust cams are used so asto be freely switched, it is possible to easily switch between thenormal combustion cycle and the Atkinson cycle, in the starting time orthe low load operating time, and the high load operating time.

[0050] (10) In the case that the internal combustion engine is providedwith the first exhaust cam having only the cam crest for the exhauststroke, and the auxiliary exhaust cam having only the cam crest forre-opening the exhaust valve in the compression stroke first stage, andthe method freely switches the single drive by means of the firstexhaust cam, and the parallel drive by means of the first exhaust camand the auxiliary exhaust cam, it is possible to easily switch betweenthe normal combustion cycle and the Atkinson cycle, in the starting timeor the low load operating time, and the high load operating time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIG. 1A is a cross sectional schematic view of a cylinder showingan air supply stroke of a control method in accordance with the presentinvention;

[0052]FIG. 1B is a cross sectional schematic view of the cylindershowing a compression stroke first stage of the control method inaccordance with the present invention;

[0053]FIG. 1C is a cross sectional schematic view of the cylindershowing a compression stroke later stage of the control method inaccordance with the present invention;

[0054]FIG. 2 is a view showing an exhaust valve lift and an air supplyvalve lift in accordance with the present invention;

[0055]FIG. 3 is a view showing an air supply valve opening period, anexhaust valve opening period and an exhaust valve re-opening period inaccordance with the present invention;

[0056]FIG. 4 is a graph showing a relation among an exhaust valve lift,an exhaust manifold pressure, an air supply manifold pressure and acylinder internal pressure at an exhaust valve re-opening time inaccordance with the present invention;

[0057]FIG. 5 is a perspective view of an exhaust cam for carrying outthe present invention;

[0058]FIG. 6 is a cross sectional view in a cross section perpendicularto an axis of the exhaust cam in FIG. 5, in which both the exhaust camsare described in parallel;

[0059]FIG. 7 is a perspective view of another exhaust cam for carryingout the present invention;

[0060]FIG. 8 is a cross sectional view in a cross section perpendicularto an axis of the exhaust cam in FIG. 7, in which both the exhaust camsare described in parallel;

[0061]FIG. 9 is a perspective view of the other exhaust cam for carryingout the present invention;

[0062]FIG. 10 is a cross sectional view in a cross section perpendicularto an axis of each of the exhaust cams in FIG. 9, in which both theexhaust cams are described in parallel;

[0063]FIG. 11 is a standard indicator diagram of an Atkinson cycle;

[0064]FIG. 12 is an indicator diagram of an Atkinson cycle in accordancewith the present invention;

[0065]FIG. 13 is a view showing a relation between compressionratio/expansion ratio and an excess air factor;

[0066]FIG. 14 is a view showing a relation between a fuel injectionpressure and a smoke;

[0067]FIG. 15 is a view showing a relation between a specific fuelconsumption and a maximum cylinder internal pressure;

[0068]FIG. 16 is a view showing a relation between the specific fuelconsumption and an NOx concentration;

[0069]FIG. 17 is a view showing a relation between a smoke index and theNOx concentration;

[0070]FIG. 18 is a view showing a relation between a supply air flowrate and a supply air pressure ratio;

[0071]FIG. 19 is a view showing a relation between an overlap period anda fresh air blow-by rate;

[0072]FIG. 20 is an index diagram of a combustion cycle in the case thatan overlap period between the exhaust valve opening period and the airsupply valve opening period is long;

[0073]FIG. 21 is an index diagram of a combustion cycle in the case thatthe overlap period between the exhaust valve opening period and the airsupply valve opening period is short;

[0074]FIG. 22 is a view showing a relation between the overlap periodand a cylinder residual gas rate;

[0075]FIG. 23A is a cross sectional schematic view of a cylinder showingan air supply stroke of an Atkinson cycle in accordance with aconventional air supply valve delayed closing;

[0076]FIG. 23B is a cross sectional schematic view of the cylindershowing a compression stroke first stage of the Atkinson cycle inaccordance with the conventional air supply valve delayed closing;

[0077]FIG. 23C is a cross sectional schematic view of the cylindershowing a compression stroke later stage of the Atkinson cycle inaccordance with the conventional air supply valve delayed closing;

[0078]FIG. 24 is a view showing an air supply valve lift correspondingto FIGS. 23A, 23B and 23C;

[0079]FIG. 25 is a view showing an air supply valve opening period andan exhaust valve opening period corresponding to FIGS. 23A, 23B and 23C;

[0080]FIG. 26 is an index diagram of the Atkinson cycle corresponding toFIGS. 23A, 23B and 23C;

[0081]FIG. 27A is a cross sectional schematic view of a cylinder showingan air supply stroke of an Atkinson cycle in accordance with aconventional air supply valve early closing;

[0082]FIG. 27B is a cross sectional schematic view of the cylindershowing an air supply stroke later stage of the Atkinson cycle inaccordance with the conventional air supply valve early closing;

[0083]FIG. 27C is a cross sectional schematic view of the cylindershowing a compression stroke of the Atkinson cycle in accordance withthe conventional air supply valve early closing;

[0084]FIG. 28 is a view showing an air supply valve opening period andan exhaust valve opening period corresponding to FIGS. 27A, 27B and 27C;and

[0085]FIG. 29 is an index diagram of the Atkinson cycle corresponding toFIGS. 27A, 27B and 27C.

BEST MODE FOR CARRYING OUT THE INVENTION

[0086]FIGS. 1A to 1C show a stroke change within a cylinder in the casethat the present invention is applied to a direct injection typemultiple cylinder diesel engine with supercharger. In an air supplystroke shown in FIG. 1A, since an air supply valve 1 is open, a supplyair pressurized by the supercharger is supplied from an air supply port2 into a combustion chamber 3. In a compression stroke first stage of apiston ascending process shown in FIG. 1B, the air supply valve 1 isclosed and an exhaust valve 5 is temporarily re-opened, therebyevacuating a compressed pressure within the combustion chamber 3 from anexhaust port 6. Further, in a compression stroke later stage shown inFIG. 1C, the exhaust valve 5 for re-opening mentioned above is closed,and the supply air is substantially compressed. In other words, acompression start time is delayed by temporarily re-opening the exhaustvalve 5 in the compression stroke first stage, thereby lowering aneffective compression ratio and preventing a maximum cylinder internalpressure from being excessively increased.

[0087]FIG. 2 shows an exhaust valve lift at a time of re-opening theexhaust valve in FIG. 1B together with an air supply valve lift. A shapeof the air supply valve lift is the same as the normal air supply valvelift which is neither the delayed closing nor the early closing, and isin a slightly open state at a compression bottom dead center BDC.

[0088] The exhaust valve at the re-opening time is structured such as tostart lifting (opening) little by little from the compression bottomdead center BDC, start closing little by little after maintaining afixed amount open state for a fixed period, and close in the middle ofthe compression stroke. This exhaust valve re-opening period correspondsto a supply air discharging period for discharging the supply air to theexhaust side.

[0089]FIG. 3 shows a relation among the exhaust valve opening period,the air supply valve opening period and the exhaust valve re-openingperiod. The exhaust valve opening period is from a later stage of anexplosion stroke to an early stage of the air supply stroke via theexhaust stroke, the air supply valve opening period is from a finalstage of the exhaust stroke to an early stage of the compression strokevia the air supply stroke, and an overlap period OL between the airsupply valve opening period and the exhaust valve opening period existsin the vicinity of an exhaust gas top dead center (a supply air top deadcenter) TDC. The exhaust valve re-opening period (the supply airdischarging period) is from the air supply bottom dead center BDC toabout a middle of the compression stroke, as described in FIG. 2.

[0090]FIG. 4 shows a relation among the exhaust valve lift, an exhaustmanifold pressure, an air supply manifold pressure and a cylinderinternal pressure at an exhaust valve re-opening time. When the exhaustgas of the other cylinders has an: influence, the exhaust manifoldpressure is temporarily higher than the air supply manifold pressure,however, the air supply manifold pressure pressurized by thesupercharger is basically higher than the exhaust manifold pressure, andin the embodiment, the re-opening period (the supply air dischargingperiod) of the exhaust valve is positioned within the period in whichthe air supply manifold pressure is higher than the exhaust manifoldpressure.

[0091] A piston ascending work such as a case of a supply air delayedclosing type Atkinson cycle is reduced by temporarily re-opening theexhaust valve so as to discharge a part of the supply air to the exhaustport, in a period in which the exhaust manifold pressure is lower thanthe air supply manifold pressure, in the compression stroke first stage,as mentioned above.

[0092]FIG. 11 is an indicator diagram showing a summary of a well-knowntheoretical Atkinson cycle (output cycle). A description will be brieflygiven of a concept of the-Atkinson cycle by utilizing FIG. 11. Referencesymbol V denotes a total volume, reference symbol V1 denotes a volume ofan adiabatic compression starting time A1, reference symbol V2 denotes avolume of an adiabatic compression finishing time A2, reference symbolV4 denotes a volume of an adiabatic expansion starting time A4,reference symbol V6 denotes a volume of an adiabatic expansion finishingtime (an exhaust valve opening time) A5, reference symbol Qv denotes aheating amount of an isovolumetric heating period (A2→A3), referencesymbol Qp denotes a heating amount of an isobaric(or isotacitc) heatingperiod (A3→A4), reference symbol Q1 v denotes a heat dissipation amountof an isovolumetric heat dissipating period (A5→A6), and referencesymbol Q1 p denotes a heat dissipation amount of an isobaric heatdissipating period (A6→A1).

[0093] Formulas of amount of heat in the respective periods mentionedabove are as follows.

[0094] Adiabatic compression period (A1→A2)

P1V1 ^(κ)=P2V2 ^(κ)

[0095] Isovolumetric heating period (A2→A3)

Qv=Cv·V 2·(Pmax−P 2)/R

[0096] Isobaric heating period (A3→A4)

Qp=Cp·Pmax·(V 4−V 2)/R

[0097] Adiabatic expansion period (A4→A5)

Pmax·V 4 ^(κ) =P 5 V 6 ^(κ)

[0098] Isovolumetric heat dissipating period (A5→A6)

Q 1 v=Cv·V 6−(P 5−P 1)

[0099] Isobaric heat dissipating period (A6→A1)

Q 1 p=Cp·P 1·(V 6−V 1)

[0100] In the above formulas, reference symbol κ is a politropicexponent, reference symbol R is a gas constant, reference symbol Cv isan isovolumic specific heat, and reference symbol Cp is an isopiesticspecific heat.

[0101] In the Atkinson cycle, a theoretic heat efficiency ηth isexpressed by the following formula.

ηth=1−(Q 1 v+Q 1 p)/(Qv+Qp)   (1)

[0102] The theoretical heat efficiency ηth is expressed by the formula(2) by introducing the relations of the amount of heat and the like andthe following relations to the formula (1) of the heat efficiency.

[0103] Engine apparent compression ratio ε=V/V2

[0104] Effective compression ratio ε′=V1/V2

[0105] EO volume ratio ν=V1/V6

[0106] Expansion ratio β=V6/V2

[0107] Effective compression ratio/expansion ratio φ=V1/V6

[0108] Explosion degree ρ=Pmax/P2

[0109] Cut.off ratio σV4/V2

ηth=1−{1/(νφε)κ)}×[νε{ρ(σφ)κ−1+κ(1−φ)}/{ρ−1+κρ(σ−1)}]  (2)

[0110] The present invention set preferably such that in the formula(2), the respective ratios are within the following ranges: EO volumeratio ν is 0.8 to 0.95, effective compression ratio/expansion ratio φ is0.5 to 0.9, and apparent compression ratio ε is 15 to 20.

[0111] [Structure of Exhaust Cam]

[0112]FIGS. 5 and 6 show an example of an exhaust cam structure forre-opening the exhaust valve in the compression stroke first stage. Inthis example, a cam crest 12 for an exhaust stroke and a cam crest 13for re-opening are formed in the same exhaust cam 11.

[0113]FIGS. 7 and 8 show another example of the exhaust cam structurefor carrying out the exhaust valve re-opening. This example is providedwith a first exhaust cam 21 having only the cam crest 12 for the exhauststroke, and a second cam 22 having the cam crest 12 for the exhauststroke and the cam crest 13 for re-opening, and both the exhaust cams 21and 22 are used so as to be freely switched. For example, at thestarting time or the low load operation time, in order to sufficientlysecure the evaporation of the fuel and improve a heat efficiency (amaximum cylinder internal pressure), it is preferable to set thecompression ratio high, so that the first exhaust cam 21 is utilized. Onthe other hand, at the high load time, the exhaust valve is re-opened inthe compression stroke first stage by utilizing the second exhaust cam22, thereby making the Atkinson cycle.

[0114]FIGS. 9 and 10 show the other example of the exhaust camstructure. This example is provided with the first exhaust cam 21 havingonly the cam crest 12 for the exhaust stroke, and an auxiliary exhaustcam 23 having only the cam crest 13 for re-opening, and the cams areused by switching between a simultaneous and parallel use of both theexhaust cams 21 and 23, and an independent use of the first exhaust cam21. For example, at the starting time or the low load operation time, inorder to sufficiently secure the evaporation of the fuel, it ispreferable to set the compression ratio high, so that only the firstexhaust cam 21 is independently used. On the other hand, at the highload time, the first exhaust cam 21 and the auxiliary exhaust cam 23 areused simultaneously and in parallel, and the exhaust valve is re-openedin the compression stroke first-stage, thereby making the Atkinsoncycle.

[0115] (Effect)

[0116]FIG. 12 is an indicator diagram of the combustion cycle in thecase of increasing the engine compression ratio, that is, the expansionratio, and temporarily re-opening the exhaust valve in the compressionstroke first stage. Reference symbol EO corresponds to an exhaust valveopening time, reference symbol SO corresponds to an air supply valveopening time, reference symbol EC corresponds to an exhaust valveclosing time, and reference symbol SC corresponds to an air supply valveclosing time, which are shown by a black circle. Further, referencesymbol REO corresponds to a start time of an exhaust valve re-opening,and reference symbol REC corresponds to a closing time (finishing time)of an exhaust valve re-opening, which are shown by a white circle. Bydelaying the compression start time to the time of REC in accordancewith the re-opening (REO→REC) of the exhaust valve, the compressionstroke corresponding to a hatched area is reduced in comparison with thecomparison stroke of the normal cycle shown by a broken line, wherebythe effective compression ratio is lowered. In accordance with theAtkinson cycle mentioned above, it is possible to enlarge the expansionratio in a state in which the maximum cylinder internal pressure ismaintained approximately in the same manner as the normal case, and theheat cycle efficiency is improved.

[0117] By aligning the timing of the exhaust re-opening, it is possibleto introduce the exhaust pulse from the other cylinders into thecylinder, whereby it is possible to achieve an internal EGR effect andit is possible to intend to reduce NOx.

[0118] By re-opening the exhaust valve in the compression stroke, it ispossible to cool the exhaust valve or the like in accordance with a blowby of the supply air, whereby it is possible to shorten the overlapperiod between the exhaust valve opening period and the air supply valveopening period while keeping the heat load of the exhaust systemconstant, a gas exchange work load is improved, it is possible toachieve a high heat efficiency, the internal EGR gas amount isincreased, and it is possible to achieve a low NOx.

[0119]FIG. 13 is a graph showing a relation between the effectivecompression ratio/expansion ratio and an excess air factor. In the caseof the normal cycle to which the Atkinson cycle is not introduced, theeffective compression ratio/expansion ratio is approximately 1. On thecontrary, the heat efficiency is improved by making the effectivecompression ratio/expansion ratio φ small to a level within a range from0.5 to 0.9 on the basis of the exhaust valve re-opening. However, sincethe excess air factor is lowered in accordance with a degree that theeffective compression ratio/expansion ratio is smaller than 1, the smokeis easily generated. In order to cope with this matter, the combustioninjection pressure is made higher than the normal one, whereby the smokeis prevented from being generated. In other words, since the combustioninjection pressure and the smoke amount are in an inversely proportionalrelation as shown in FIG. 14, it is possible to achieve an improvementof the heat efficiency and a reduction of the smoke amount, byincreasing the injection pressure while lowering the effectivecompression ratio/expansion ratio φ to the range from 0.5 to 0.9 asmentioned above.

[0120]FIG. 15 shows a relation between a specific fuel consumption and amaximum cylinder internal pressure. A black circle position {circle over(1)} corresponds to the case of the normal cycle to which the Atkinsoncycle is not introduced, a black triangle position {circle over (5)}corresponds to a state in which the OL period is shortened and thesupply air pressure is increased at the same time when the Atkinsoncycle is introduced in accordance with the present invention. In theposition {circle over (5)}, it is possible to widely lower the specificfuel consumption in comparison with the position {circle over (1)}, andit is possible to restrict the increase of the maximum cylinder internalpressure to an allowable level in a point of a strength or the like.

[0121] A white square position {circle over (2)} and a white triangularposition {circle over (3)} correspond to a conventional approach forimproving the heat efficiency. The position runs from the position{circle over (1)} to the position {circle over (2)} along an arrow G1 byincreasing the compression ratio and shortening the OL period, andfurther runs to the position {circle over (3)} along an arrow G3 byincreasing the supply air pressure. In the position {circle over (2)},the maximum cylinder internal pressure is increased to an allowablelevel in a point of the strength or the like, however, the specific fuelconsumption is hardly lowered. In the position {circle over (3)}, thespecific fuel consumption is widely lowered, however, the maximumcylinder internal pressure is excessively increased to a level in whicha lack of strength is generated.

[0122] A black square position {circle over (4)} corresponds to a statein which the Atkinson cycle is introduced from the position {circle over(1)} in accordance with the present invention and the OL period isshortened. The cylinder internal pressure is lowered to the same levelas that of the normal cycle in the position {circle over (1)}, incomparison with the position {circle over (2)} in the conventionalexample, as shown by an arrow G2, and the specific fuel consumption islowered in comparison with the position {circle over (2)}.

[0123] The position runs to the position {circle over (5)} by making thesupercharged pressure higher from the state in the position {circle over(4)} mentioned above, however, the specific fuel consumption is widelylowered as shown by an arrow G5, and the increase of the cylinderinternal pressure can be restricted to the increase about the position{circle over (2)} mentioned above.

[0124] In this case, the position also runs to the position {circle over(5)} as shown by an arrow G4, by introducing the Atkinson cycle inaccordance with the present invention from the position {circle over(3)}.

[0125]FIG. 16 is a graph showing a relation between the specific fuelconsumption and the NOx. A black circle position {circle over (1)}corresponds to the case of the normal cycle which does not employ theAtkinson cycle, a black square position {circle over (2)} corresponds tothe case to which the Atkinson cycle is introduced in accordance withthe present invention without changing the supercharged pressure fromthe position {circle over (1)} mentioned above. In the position {circleover (2)}, the NOx is reduced, however, the specific fuel consumption isa little increased. In accordance with an increase of the supply airpressure, it is possible to widely reduce the specific fuel consumptionwhile restricting the NOx to the same level as that of the position{circle over (1)}, as shown by a black triangle position {circle over(3)}.

[0126]FIG. 17 is a graph showing a relation between a smoke index andthe NOx. Positions {circle over (1)}, {circle over (2)} and {circle over(3)} have the corresponding conditions to those in FIG. 16. The position{circle over (2)} corresponds to the case to which the Atkinson cycle isintroduced without changing the supercharged pressure from the position{circle over (1)} corresponding to the normal cycle. In this position,the NOx is reduced, however, the smoke is increased. On the contrary, itis possible to restrict the NOx and the smoke to the same level as thoseof the actual position {circle over (1)} as in the position {circle over(3)}, by increasing the supply air pressure.

[0127]FIG. 18 is an index of a working state of a superchargercompressor. FIG. 18 is a graph showing a supply air pressure ratio by avertical axis and a compressor efficiency and a surging line withrespect to a supply air flow rate by a horizontal axis. In this drawing,reference symbol B1 shows a case of the normal cycle to which theAtkinson cycle is not introduced, reference symbol B2 shows a case thatthe Atkinson cycle is formed by the air supply valve delayed closing orthe air supply valve early closing, reference symbol B3 shows a casethat the Atkinson cycle is formed by the re-opening of the exhaust valvein accordance with the present invention, and reference symbol B4 showsa surging line of the supercharger.

[0128] In FIG. 18, in the Atkinson cycle formed by the air supply valveearly closing or the air supply valve delayed closing, since the supplyair is returned from the air supply valve to the air supply port even inthe case that the supply air pressure ratio is increased by increasingthe supercharged pressure, only the supercharged pressure is increasedand the supply air flow rate is not increased as shown by the point B2,and the point comes close to the surging line B4 of the supercharger, sothat it is impossible to efficiently utilize the supercharger.

[0129] On the other hand, in the case of the Atkinson cycle formed bythe re-opening of the exhaust valve in accordance with the presentinvention, since the supply air is discharged to the exhaust port alongthe flow of the supply air, the supply air flow rate is increasedtogether with the supply air pressure ratio by increasing thesupercharged pressure. Accordingly, the point does not come close to thesurging line B4 as is different from the point B3, and it is possible toefficiently utilize the supercharger.

[0130]FIG. 19 is a graph showing a relation between the overlap period(the period OL in FIG. 3) between the exhaust valve opening period andthe air supply valve opening period, and a fresh air blow by rate. Amass-produced cam in a graph D1 corresponds to a case of the normalcycle which is not formed as the Atkinson cycle, and a fresh air blow byrate in this case is set to 1.

[0131] In the case that the overlap period OL is long, an atrophiedstate is formed from an air supply valve opening period SO to an exhaustvalve closing period EC as shown in FIG. 20, a hatched area becomessmall, and a loss of heat efficiency is generated. On the other hand, inthe case that the overlap period OL is simply shortened, it is possibleto secure a rising edge L from the air supply valve opening period SO tothe exhaust valve closing period EC as shown in FIG. 21, whereby it ispossible to secure the hatched area large, and the heat efficiency isimproved, however, the fresh air blow by rate is widely reduced as shownby a graph D2 in FIG. 19, and the exhaust gas temperature becomes toohigh.

[0132] On the contrary, in the case that the overlap period OL isshortened as shown by a graph D3, and the re-opening period (a range ofa crank angle θ1 in FIG. 3) in the compression stroke first stage of theexhaust valve is executed by 60 degree in accordance with the presentinvention, it is possible to obtain the fresh air blow by rate in thesame manner as that of the conventional mass-produced cam D1 as shown inFIG. 19, as well as it is possible to obtain the improvement of the heatefficiency as described in FIG. 21, so that it is possible to preventthe exhaust gas temperature from being increased, and it is possible tomaintain the exhaust gas load constant.

[0133] In the case that the overlap period OL is shortened as shown by agraph D4, and the re-opening period (a range of θ1 in FIG. 3) in thecompression stroke first stage of the exhaust valve is increased to 90degree, it is possible to obtain the improvement of the heat efficiencyas described in FIG. 21, however, there is a tendency that the fresh airblow by amount is increased too much in the exhaust valve re-openingperiod.

[0134] Accordingly, in preferable, it is possible to achieve theimprovement of the heat efficiency, prevention of the exhaust gastemperature from being increased and prevention of the fresh air blow byfrom being too much, by setting the exhaust valve re-opening period θ1in FIG. 3 to about 30 to 60 degree, as well as shortening the overlapperiod OL.

[0135]FIG. 22 shows a relation between a cylinder residual gas rate andthe overlap period OL. When the overlap period OL is shortened, thecylinder residual gas rate is increased, whereby it is possible toachieve the internal EGR effect and it is possible to intend to reducethe NOx.

[0136] (Industrial Applicability)

[0137] The present invention can be also utilized in gas and gasolinedirect injection type internal combustion engines.

1. A method of controlling an internal combustion engine, wherein aneffective compression ratio is decreased by temporarily opening anexhaust valve in a compression stroke first stage while driving which isnot while starting or driving under a low load.
 2. A method ofcontrolling an internal combustion engine as claimed in claim 1, whereinan effective compression ratio is changed by a range from 0.5 to 0.9times of the expansion ratio. 3 (Cancelled)
 4. A method of controllingan internal combustion engine as claimed in any one of claims 1 or 2,wherein the internal combustion engine is provided with a first exhaustcam having only a cam crest for an exhaust stroke, and a second exhaustcam having a cam crest for the exhaust stroke and a cam crest for againopening the exhaust valve in the compression stroke first stage, andboth the exhaust cams are arranged so as to be freely switched.
 5. Amethod of controlling an internal combustion engine as claimed in anyone of claims 1 or 2, wherein the internal combustion engine is providedwith a first exhaust cam having only a cam crest for an exhaust stroke,and an auxiliary exhaust cam having only a cam crest for again openingthe exhaust valve in the compression stroke first stage, and the methodfreely switches a single drive by means of the first exhaust cam, and aparallel drive by means of the first exhaust cam and the auxiliaryexhaust cam.
 6. A method of controlling an internal combustion engine asclaimed in claim 4, wherein the internal combustion engine is providedwith a first exhaust cam having only a cam crest for an exhaust stroke,and an auxiliary exhaust cam having only a cam crest for again openingthe exhaust valve in the compression stroke first stage, and the methodfreely switches a single drive by means of the first exhaust cam, and aparallel drive by means of the first exhaust cam and the auxiliaryexhaust cam.